Jumps and drops
Trajectory during a drop (the trajectory is only the descending branch of a parabola) and a jump (the trajectory is a parable)
How many videos we've seen of riders being shot upwards from huge ramps in bike parks, or launched down into a canyon void at full speed. Jumps and drops are essential elements for our excursions and have particular characteristics that are mentioned in what follows, referring to the book "The science of Mountain Bike riding: the physics behind MTB skills".
First of all, a jump and a drop are two different things that need completely different body movements. The substantial difference between the two is that during a jump the bike-rider system performs a complete parabolic trajectory, consisting of ascending and descending parabola branches. With the drop, however, the rider performs only the descending branch. It follows that during a jump the bike-rider system must rotate in the air more than with a drop: the ground support plane of the mountain bike goes from the upwards inclined starting ramp to the downwards inclined landing one.
It is therefore clear why the technique required to deal with them is very different. Although there are several ways, generally to perform a jump you need to resort to the bunny hop technique: on the launch pad the bike tilts upwards and the body remains upright extending on its feet, possibly with an upward momentum; when in the air, the bike is induced to rotate forward, in order to land with the front wheel slightly in advance. During the drop, since you do not have large variations of inclination of the bike, it is enough for the body to move back slightly the moment you lose contact with the ground, to reduce the rotational thrust of the weight, which has a tipping effect, and prepare the body to absorb the landing impact.
First of all, a jump and a drop are two different things that need completely different body movements. The substantial difference between the two is that during a jump the bike-rider system performs a complete parabolic trajectory, consisting of ascending and descending parabola branches. With the drop, however, the rider performs only the descending branch. It follows that during a jump the bike-rider system must rotate in the air more than with a drop: the ground support plane of the mountain bike goes from the upwards inclined starting ramp to the downwards inclined landing one.
It is therefore clear why the technique required to deal with them is very different. Although there are several ways, generally to perform a jump you need to resort to the bunny hop technique: on the launch pad the bike tilts upwards and the body remains upright extending on its feet, possibly with an upward momentum; when in the air, the bike is induced to rotate forward, in order to land with the front wheel slightly in advance. During the drop, since you do not have large variations of inclination of the bike, it is enough for the body to move back slightly the moment you lose contact with the ground, to reduce the rotational thrust of the weight, which has a tipping effect, and prepare the body to absorb the landing impact.
Now let's see what are the characteristics that jumps and drops have in common.
The first is the physical condition in which the rider is located when flying in the air, called "free fall". This condition occurs when an object falls attracted by the earth's gravitational force alone, i.e. dragged down only by its weight. The most interesting aspect is that those who are in this condition feel weightless as if there were no gravity.
The second aspect in common between jumps and drops is that in the air the bike-rider system is in the conditions of validity of the "principle of conservation of angular momentum" which substantially binds the speed of rotation of the system to the spatial distribution of the masses and therefore to the position of the rider. Like the dancer who manages to rotate more or less quickly by changing the body configuration, the rider, stretching or crouching on the bike, slows down or increases the speed of rotation of the system. Knowing how to manage the speed of rotation in the air allows the rider to reduce the risk of overturning (over-rotation) or landing on the rear (under-rotation), especially for those who make long-range acrobatic jumps.
Finally, a third interesting aspect is the importance of movements the moment you detach from the ground. As regards the trajectory, which depends exclusively on the speed, and the rotation of the bike-rider system, everything is mathematically defined at the moment of detachment from the ground. In the air, therefore, we do not have much room to maneuver and we can only hope that we have made the right movements before.
Below is the video "Jumps and Freefall"
For any information, to suggest a topic or to simply have your say, find the contacts you can write to.
The first is the physical condition in which the rider is located when flying in the air, called "free fall". This condition occurs when an object falls attracted by the earth's gravitational force alone, i.e. dragged down only by its weight. The most interesting aspect is that those who are in this condition feel weightless as if there were no gravity.
The second aspect in common between jumps and drops is that in the air the bike-rider system is in the conditions of validity of the "principle of conservation of angular momentum" which substantially binds the speed of rotation of the system to the spatial distribution of the masses and therefore to the position of the rider. Like the dancer who manages to rotate more or less quickly by changing the body configuration, the rider, stretching or crouching on the bike, slows down or increases the speed of rotation of the system. Knowing how to manage the speed of rotation in the air allows the rider to reduce the risk of overturning (over-rotation) or landing on the rear (under-rotation), especially for those who make long-range acrobatic jumps.
Finally, a third interesting aspect is the importance of movements the moment you detach from the ground. As regards the trajectory, which depends exclusively on the speed, and the rotation of the bike-rider system, everything is mathematically defined at the moment of detachment from the ground. In the air, therefore, we do not have much room to maneuver and we can only hope that we have made the right movements before.
Below is the video "Jumps and Freefall"
- Should you behave the same way with all kinds of drops ?
- When can the ramps kick and cause tipping ?
- What is the difference between a jump and a bunny hop ?
- What are the parameters that allow a soft landing ?
- ...
For any information, to suggest a topic or to simply have your say, find the contacts you can write to.